The present invention relates to a fuel injection timing apparatus or timer for use with a fuel injection pump.
In recent years, it has become a tendency in diesel engines to delay the fuel injection timing in comparison with that heretofore in use for the purpose of reducing NOx in particular. According to such method, however, although reduction of Nox can be promoted, other problems are caused. Specifically, the starting performance of an engine is deteriorated, especially at low temperatures, and also white smoke may be exhausted during idling of the engine.
To cope with the above problems, there has been proposed a fuel injection timing apparatus which is capable of adjusting the injection timing in correspondence with temperatures when an engine is started, as disclosed in Japanese Utility Model Examined Publication No. 59-36670. The invention related to this publication has also been assigned to one of the assignees of the invention of the present application. The apparatus disclosed in this publication comprises weights adapted to rotate synchronously with the engine so as to advance the injection timing in proportion to the degree of their movement, pins fixed to the weights, and a rod having a cam surface for urging the pins which rod is driven in correspondence with ambient temperatures. The apparatus is operated such that, when the engine is started at a low temperature, the weights are forcibly moved or opened through the pins.
In the apparatus according to the above publication, since the weights are biased always in a direction toward their closed position by means of springs, an extremely great driving force is required for moving, against the biasing force, the pins and the weights from a state in which the weights are fully closed toward their open position. This gives rise to another problem that a driving mechanism for the rod becomes large in size and, accordingly, the fuel injection timing apparatus is enlarged as a whole.